1. Field of the Invention
The present invention relates to an optical temperature sensor and a method of controlling the optical temperature sensor.
2. Description of the Related Art
Conventionally, various optical temperature sensors have been proposed. For example, an optical temperature sensor is known that includes a temperature sensing portion that detects a temperature from a change of an energy gap in response to a temperature change. This optical temperature sensor causes a measuring beam emitted from a first light emitting device and a reference beam emitted from a second light emitting device to pass through the temperature sensing portion, and measures an external temperature based on light intensities of reflected light of the measuring beam and reflected light of the reference beam that have passed through the temperature sensing portion.
Japanese Laid-Open Patent Application Publication No. 62-118227 discloses a fiber optic temperature sensor capable of reducing an influence on a temperature measurement value without respect to a variation of the transmitting efficiency of an optical transmission line. Japanese Laid-Open Patent Application Publication No. 6-137965 discloses a method for measuring a temperature by using an optical temperature sensor that can remove a change of a light intensity caused by disturbance from the temperature measurement value.
However, even if the light intensities of the measuring beam and the reference beam that are measured at light emitting parts have no dispersion, light intensities of the measuring beam and the reference beam that are measured at light receiving parts may have dispersion due to an individual difference of the light emitting parts or optical fiber cables. The optical fiber cables lead the measuring beam and the reference beam output from the light emitting parts to the temperature sensing portion, and further lead the measuring beam and the reference beam reflected by the temperature sensing portion to the light receiving parts. When the dispersion causes the light intensities of the measuring beam and the reference beam that are measured at the light receiving parts to be out of a normal range, the measurement accuracy of the temperature decreases.
With respect to this problem, the above technology does not consider how to compensate for the individual difference between parts themselves constituting the temperature sensor or the individual difference caused by a combination of a plurality of parts and to keep the measurement accuracy of the temperature higher than a certain level. For example, the “disturbance” in Japanese Laid-Open Patent Application Publication No. 6-137965 does not include the individual difference of the parts constituting the temperature sensor.